Background: Birth defect registries are often used for etiological research. Either as hypotheses-generating studies, or studies directed at one specific association between a risk factor and a birth defect in order to confirm or refute possible associations. Methods: A literature search in Medline was performed looking for studies using birth defect registries for studying different risk factors. Results: A brief summary of study design for etiological research with registration data is given. Subsequently, the different studies performed are discussed according to the risk factors investigated. Different aspects of the studies are listed and discussed. For each of the risk factors, the usefulness of birth defect registries to study the specific risk factor is discussed. Registries are dependent on the factors that are included in the registry or recorded in different databases. Most studies have looked at risk factors with readily available data, such as maternal age, illnesses and drugs. There is also wide use of other registers with exposure data on, for example, the environment. Conclusions: Birth defect registries have been used in the evaluation of many possible risk factors for birth defects. They have also been used in rebutting alarms in the media on possible clusters and risk factors.